The present invention relates to a projection-type display apparatus such as a liquid crystal projector, or in particular to the correction of a trapezoidal distortion.
In recent years, conferences are often held for a presentation, in which the presentation data prepared in a personal computer are projected on a presentation screen in an enlarged form using a liquid crystal projector or the like without being distributed to attendants.
In an enlarged projection using a liquid crystal projector, the projection screen is generally displayed without any distortion when the image is projected from the front of the screen, i.e. from the direction perpendicular to the screen surface. In the case where the image is projected in a direction not perpendicular to the screen surface, on the other hand, the projection screen is displayed in distorted form. This distortion is generally called a trapezoidal distortion. The trapezoidal distortion is corrected by either an optical method or an electrical method. The optical method is not widely used as it is structurally limited and expensive. In the electrical method which is generally used now, on the other hand, the trapezoidal distortion is corrected by digitally processing the video signal and distorting the image reversely. In most cases using the electrical method, the user has so far manually adjusted the image while watching the distorted screen. However, a method for conducting the image adjustment automatically is reported (for example, JP-A-2000-122617).
According to the aforementioned patent publication, the trapezoidal distortion is automatically corrected by detecting the distance to the screen using a plurality of distance sensors and determining the angle of inclination between the screen and the display apparatus based on the result of detection.